Theoretical and experimental studies will be conducted on single fibers of straited muscles. The theoretical effort will focus on the development of expressions for the diffraction of light by the regular patterns of a muscle fiber. A vector field with proper polarization consideration will be used for the light wave. The muscle fiber will be treated in a model which includes the cylindrical geometry of the fiber, the possible myofibril skewness in alignment, the possible sarcomere filament length variation, the filament overlap conditions and contributions from the anisotropic elements to diffraction. Experimentally, anisotropic diffraction pattern will be investigated in detail. This diffraction intensity pattern and its time correlation spectrum will be obtained. From these sudies, a sensitive new probe for studying the dynamics and conformation changes of the optically anisotropic elements will have been established. In particular, s-2 movements under states of muscular activity will be probed.